Epilepsy is a common but often devastating neurological condition where abnormal brain excitation leads to uncontrolled and unpredictable loss of normal function often ending in a tonic-clonic seizure. In a majority of cases the seizures are initiated in a small region of the brain with no clear underlying genetic or structural defect. This "epileptic focus" can be localized and surgically removed to potentially cure the seizures. Exactly what makes and maintains certain areas of human neocortex epileptic is not known, nor is it known what structural and functional changes occur that lead to and maintain this state. One possibility that has gained increasing attention is that these changes come about through activity-dependent changes in pathways that are initiated through growth and differentiation factors. These factors act through signaling intermediates to regulate transcription factors that turn on genes that can make the cortex hyperexcitable. Using subdural recording electrodes to map human neocortical epileptic foci in children with intractable seizures, a high-throughput screening method that combines focused, high-density cDNA arrays with wide searching oligonucleotide arrays was used to identify genes differentially expressed at epileptic foci compared to nearby areas with no independent epileptiform activity. Using these methods two important signaling pathways were identified; one initiated by neurotrophins (BDNF) and the other by neuregulin. These factors activate the NFkB and ETS-2 transcription factors, respectively, which in turn regulate proteins known to modulate neuronal excitability. The studies proposed here will measure the differential expression of neurotrophin and neuregulin signaling pathway genes in human epileptic tissues using real-time RT-PCR, in situ hybridization, and immunohistochemistry and will extend these important findings to a larger series of patients using cDNA and oligonucleotide microarrays. The hypothesis is that these gene expression changes correlate directly with electrical activity and will be found in regions of seizure spread and along interictal gradients of epileptiform activity. These changes would then induce and maintain the hyperexcitable state of the tissue. Understanding activity-dependent expression of regulatory genes together with defining the cell types expressing these genes will provide insights into how seizures develop in humans that will aid in clinical management and reveal new therapeutic avenues for patients with epilepsy.